Set the amount of hair strands. Use as little particles as possible,
especially if you plan to use soft body animation later.
But you need enough particles to have good control.
For a “normal” haircut I found some thousand (very roughly 2000) particles to give enough control.
You may need a lot more particles if you plan to cover a body with fur.
Volume will be produced later with Children.

Hair Length

Controls how long the hair are.

Emit From

Vertices

Emits hair particles from the vertices of a mesh.
When using this the distribution settings (see below) are not available.

Faces

Emits hair particles from the surface of a mesh’s faces.

Volume

Emits hair particles from the volume of an enclosed mesh.

Random

Hair particles are emitted in a random order.

Even Distribution

Hair particle distribution is made even based on surface area of the elements,
i.e. small elements emit less particles than large elements, so that the particle density is even.

Distribution

Jittered

Particles are placed at jittered intervals on the emitter elements.

Particles/Face

Number of emissions per face (0 = automatic).

Jittering Amount

Amount of jitter applied to the sampling.

Random

Particles are emitted from random locations in the emitter’s elements.